Fuel comprising an emulsion between water and a liquid hydrocarbon

ABSTRACT

Fuel comprising an emulsion between water and a liquid hydrocarbon, said emulsion being stabilized by adding a polymeric surfactant obtainable by reaction between: (i) a polyolefin oligomer functionalized with at least one group deriving from a dicarboxylic acid, or a derivative thereof; and (ii) a polyoxyalkylene comprising linear oxyalkylene units, said polyoxyalkylene being linked to a long-chain alkyl group optionally containing one or more ethylenic unsaturations. The fuel has high stability over time, without forming carbonaceous deposits which adhere to metal surfaces.

[0001] The present invention relates to a fuel comprising an emulsionbetween water and a liquid hydrocarbon. More particularly, the presentinvention relates to a fuel comprising an emulsion between water and aliquid hydrocarbon, this emulsion being stabilized by adding anemulsifier.

[0002] It is known that the combustion of liquid hydrocarbons, forexample for feeding internal combustion engines or for producing heat,leads to the formation of numerous pollutants, in particular soot,particulates, carbon monoxide (CO), nitrogen oxides (NOx), sulphuroxides (SOx), and noncombusted hydrocarbons, which contributesignificantly towards atmospheric pollution.

[0003] It is also known that the addition of controlled amounts of waterto fuel can significantly reduce the production of pollutants. It isbelieved that this effect is the result of various phenomena arisingfrom the presence of water in the combustion zone. For example, thelowering of the peak combustion temperature by water reduces theemission of nitrogen oxides (NOx), the formation of which is promoted byhigh temperatures. In addition, the instantaneous vaporization of thewater promotes better dispersion of the fuel in the combustion chamber,thereby significantly reducing the formation of soot, particulates andCO. These phenomena take place without adversely affecting the yield forthe combustion process.

[0004] Several solution have been proposed in attempts to add water toliquid fuel at the time of use, that is to say just before the fuel isinjected into the combustion chamber, or directly into the chamberitself. However, these solutions require modifications to be made to thestructure of the combustion apparatus and are not capable of achievingoptimum dispersion of the water in the fuel, which is an essentialrequisite for obtaining a significant reduction in pollutants withoutcompromising the calorific yield for the process.

[0005] Thus, the most promising and numerous efforts made hitherto weredirected towards the formulation of emulsions between liquidhydrocarbons and water in the presence of emulsifiers (surfactants) forthe purpose of uniformly dispersing the water in the hydrocarbon phasein the form of micelles of the smallest possible size.

[0006] For example, patent EP-A-475 620 describes microemulsions of adiesel fuel with water, which contain a cetane improver and anemulsifying system comprising a hydrophilic surfactant and a lipophilicsurfactant. These surfactants are selected from ethoxylated C₁₂-C₁₈alkylammonium salts of a C₉-C₂₄ carboxylic or sulphonic acid: thehydrophilic surfactant contains at least six ethylene oxide units, whilethe lipophilic surfactant contains less than six ethylene oxide units.

[0007] Patent EP-A-630 398 describes a fuel in the form of an emulsionconsisting of a hydrocarbon fuel, from 3 to 35% by weight of water andat least 0.1% by weight of an emulsifying system consisting of asorbitan oleate, a polyalkylene glycol and an ethoxylated alkylphenol.

[0008] Patent application WO 97/34969 describes an emulsion betweenwater and a hydrocarbon, for example a diesel fuel. This emulsion isstabilized by adding an emulsifier consisting of a sorbitansesquioleate, a polyethylene glycol monooleate and an ethoxylatednonylphenol. This emulsifier has an overall HLB (hydrophilic-lipophilicbalance) value of between 6 and 8.

[0009] A process for producing a stabilized emulsion of a liquid fueland water is described in patent EP-A-812 615. This process involvespreparing a first emulsion by mixing the fuel, the water and asurfactant, and subsequently mixing the emulsion thus obtained with morewater to give the final emulsion. The emulsion is stabilized using ahydrophilic surfactant or a lipophilic surfactant, or a mixture thereof.Lipophilic surfactants which can be used are fatty acid esters ofsorbitol, for example sorbitan monooleate, while hydrophilic surfactantswhich are suitable for this purpose are fatty acid esters of sorbitolcontaining a polyoxyalkylene chain, for example polyoxyethylene sorbitantrioleate. Further stabilization of the emulsion can be obtained byadding ethylene glycol or a polyethylene glycol.

[0010] Patent application WO 92/19701 describes a process for reducingthe emission of NOx from a gas turbine, in which an emulsion of waterwith a diesel fuel is used. The emulsion is stabilized by adding anemulsifier selected from: alkanolamides obtained by condensing analkylamine or hydroxyalkylamine with a fatty acid; and ethoxylatedalkylphenols. The emulsifier preferably has an HLB value of less than orequal to 8. Physical stabilizers such as waxes, cellulose derivatives orresins can be added to improve the stability. As described in patentapplication WO 93/07238, the above emulsion can be further stabilized byadding a difunctional block polymer with a primary hydroxyl end group,in particular a copolymer containing propylene oxide/ethylene oxideblocks.

[0011] On the basis of the Applicant's experience, the possibilities ofsuccess in the use of fuels in the form of an emulsion between water anda liquid hydrocarbon are mainly associated with the possibility ofreplacing a conventional liquid fuel with an emulsified fuel without theneed for any structural changes to the combustion apparatus and withoutadversely affecting the correct functioning of this apparatus.

[0012] In particular, the fuel in emulsion form requires high stabilityover time in a broad temperature range (for example for at least threemonths under normal storage conditions, i.e. between −20° C. and +50°C.), so as to avoid, during residence in tanks, the formation of awater-rich phase which tends to become deposited at the bottom of thetank. Feeding this aqueous phase into the combustion chamber would bringabout a considerable impairment in the performance level of the engine,or even permanent damage thereto.

[0013] In addition, the Applicant has found that the addition ofemulsifiers to improve the stability of the emulsion can lead, duringcombustion, to the formation of carbonaceous deposits which adhere tothe internal surface of the combustion chamber and to the injectors.This phenomenon can adversely affect the running of the engine, as aresult of which frequent maintenance is necessary to remove thesedeposits.

[0014] The Applicant has now found that fuels comprising an emulsionbetween water and a liquid hydrocarbon can be produced using a polymersurfactant as defined below as emulsifier. The fuel thus obtaineddisplays high stability over time in a broad temperature range, withoutforming carbonaceous deposits that adhere to the metal surfaces.

[0015] In a first aspect, the present invention thus relates to a fuelcomprising an emulsion between water and a liquid hydrocarbon, thisemulsion being stabilized by an emulsifier, characterized in that thesaid emulsifier is a polymeric surfactant obtainable by reactionbetween: (i) a polyolefin oligomer functionalized with at least onegroup deriving from a dicarboxylic acid, or a derivative thereof; and(ii) a polyoxyalkylene comprising linear oxyalkylene units, saidpolyoxyalkylene being linked to a long-chain alkyl group optionallycontaining one or more ethylenic unsaturations.

[0016] In a further aspect, the present invention relates to a processfor fueling a combustion apparatus comprising at least a combustionchamber, comprising: feeding a fuel to said at least one combustionchamber; igniting said fuel in said at least one combustion chamber;

[0017] wherein said fuel comprises an emulsion between water and aliquid hydrocarbon as described above.

[0018] Preferably, said combustion apparatus is an internal combustionengine.

[0019] Preferably, the polyolefin oligomer has an average molecularweight of from 300 to 10,000, preferably from 500 to 5000.

[0020] The polyolefin oligomer is generally obtained byhomopolymerization or copolymerization of one or more olefins containingfrom 2 to 16 carbon atoms, selected, for example, from:

[0021] α-olefins, i.e. olefins in which the double bond is in theterminal position, such as: ethylene, propylene, 1-butene, isobutene,4-methyl-1-pentene, 1-hexene, 1-octene, 2-methyl-1-heptene and the like;

[0022] internal monoolefins, i.e. olefins in which the double bond isnot in a terminal position, such as: 2-butene, 3-pentene, 4-octene andthe like.

[0023] The said olefins can moreover be copolymerized with otherhydrocarbons containing at least one ethylenic unsaturation, such asmonovinylarenes (for example styrene, p-methylstyrene and the like) orconjugated dienes (for example 1,3-butadiene, isoprene, 1,3-hexadieneand the like).

[0024] Preferably, the polyolefin oligomer derives from thepolymerization of mixtures of olefins containing 4 carbon atoms,generally containing from 35 to 75% by weight of 1-butene and from 30 to60% by weight of isobutene, in the presence of a Lewis acid as catalyst,for example aluminium trichloride or boron trifluoride. Thesepolymerization products are generally known as “polyisobutenes” sincethey mainly contain isobutene repeating units of formula:

[0025] The amount of isobutene units is usually not less than 80 mol %.

[0026] The polyoxyalkylene comprises linear oxyalkylene units whichimpart hydrophilic properties, in particular units of formula —CH₂CH₂O—or —CH₂CH₂CH₂O—.

[0027] The number of linear oxyalkylene units is predetermined mainly asa function of the nature and length of the lipophilic portions presentin the polymeric surfactant, in particular of the polyolefin oligomerand the long-chain alkyl group.

[0028] Preferably, the polyoxyalkylene is a polyoxy-ethylene containingfrom 2 to 40 and preferably from 5 to 20 oxyethylene units of formula—CH₂CH₂O—.

[0029] Alternatively, the polyoxyalkylene is a copolymer containing from2 to 30 and preferably from 5 to 15 oxyethylene units of formula—CH₂CH₂O—, and not more than 12, preferably from 1 to 10, branchedoxyethylene units of formula:

[0030] wherein R₁ is an alkyl containing from 1 to 3 carbon atoms.Preferably, R₁ is methyl.

[0031] In the case of copolymers, the oxyalkylene units are distributedalong the chain randomly, in blocks or alternately. The number ofoxyalkylene units is expressed as the average number of units per chain.

[0032] The polyoxyalkylene is linked to a long-chain alkyl group. Thisalkyl group, of linear or branched structure, optionally containing oneor more ethylenic unsaturations, generally contains from 8 to 24 carbonatoms.

[0033] The link between the polyoxyalkylene and the long-chain alkylgroup is preferably made by an ester group or an ether group, and can beobtained by:

[0034] (a) condensing a polyoxyalkylene (poly-alkylene glycol) with afatty acid or a derivative thereof, in particular an ester, withformation of the corresponding polyoxyalkylene monoester;

[0035] (b) esterification of a fatty alcohol with an alkylene oxide, inparticular with ethylene oxide or mixtures of ethylene oxide andpropylene oxide.

[0036] Examples of fatty acids which can be used in reaction (a) are:myristoleic acid, palmitoleic acid, oleic acid, gadoleic acid, erucicacid, ricinoleic acid, linoleic acid, linolenic acid, arachidonic acid,lauric acid, myristic acid, palmitic acid, stearic acid, behenic acidand the like, or mixtures thereof.

[0037] Examples of fatty alcohols which can be used in reaction (b) are:octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetylalcohol, octadecyl alcohol, oleyl alcohol, linoleyl alcohol, linolenylalcohol and the like, or mixtures thereof.

[0038] The polyolefin oligomer is functionalized by reaction with adicarboxylic acid, or a derivative thereof. In particular, thefunctionalization can be carried out by:

[0039] (i) concerted reaction of “ene” type between the polyolefinoligomer containing at least one ethylenic unsaturation and adicarboxylic acid derivative containing an ethylenic unsaturation;

[0040] (ii) anionic condensation reaction between the polyolefinoligomer functionalized with a leaving group (for example a halogen atomor a tosyl or mesyl group) and a saturated dicarboxylic acid derivative.

[0041] In both cases, acyl halides (preferably chlorides or bromides),C₁-C₄ esters or, preferably, anhydrides can be used as dicarboxylic acidderivatives.

[0042] The dicarboxylic acid containing an ethylenic unsaturation can beselected, for example, from: maleic acid, fumaric acid, citraconic acid,itaconic acid and the like, or mixtures thereof.

[0043] The saturated dicarboxylic acid can be selected, for example,from: malonic acid, succinic acid, glutaric acid, adipic acid,2-hexene-1,6-dioic acid, azelaic acid and the like, or mixtures thereof.

[0044] Preferably, the functionalized polyolefin oligomer derives fromthe reaction between maleic anhydride and a polyisobutene containing notless than 65 mol %, preferably not less than 80 mol %, of exo doublebonds, i.e. vinylidene groups of formula:

[0045] Polyisobutenes of this type are available, for example, under thebrand names Ultravis® (BP Amoco Chemicals) and Glissopal® (BASF).

[0046] Further details regarding the preparation of polyolefin oligomersfunctionalized as described above are given, for example, in U.S. Pat.Nos. 4,152,499 and 5,567,344.

[0047] The condensation reaction between the functionalized polyolefinoligomer and the polyoxy-alkylene bonded to a long-chain alkyl group canbe carried out in bulk or in the presence of an organic solvent.Preferably, for the purpose of helping to remove the water deriving fromthe condensation, the organic solvent is selected from those which forman azeotrope with water, for example toluene or xylene, or mixturesthereof. The condensation reaction can be carried out at a temperaturewhich is generally not greater than 200° C. When an organic solvent isused, the reaction temperature is usually not greater than the boilingpoint of this solvent. The reaction time can vary within a wide range,generally between 3 and 24 hours.

[0048] The amount of polymeric surfactant to be used in the fuelaccording to the present invention is predetermined mainly as a functionof the amount of water to be emulsified and the type of liquidhydrocarbon used. Preferably, the polymeric surfactant as defined aboveis present in the fuel in an amount of between 0.1 and 5% by weight,preferably between 0.5 and 3% by weight, relative to the total weight ofthe fuel.

[0049] It should be noted that the polymeric surfactant as defined aboveis capable of effectively stabilizing the emulsion over a broadtemperature range without the addition of further emulsifiers. However,this is not to exclude the possibility of adding other products whichmay in some way modify the stability of the emulsion, in particularother emulsifiers known in the art.

[0050] The type of emulsion obtainable by using the polymeric surfactantas defined above is generally of the water-in-oil type, wherein thewater particles are dispersed in the continuous hydrocarbon phase. It isbelieved that this type of emulsion ensures maximum efficiency in thereduction of pollutants on account of the water present during thecombustion phase.

[0051] The fuel according to the present invention includes a liquidhydrocarbon, generally deriving from the distillation of petroleum andconsisting essentially of mixtures of aliphatic, naphthenic, olefinicand/or aromatic hydrocarbons. The liquid hydrocarbon generally has aviscosity at 40° C. of between 1 and 53 cSt, and a density at 15° C. ofbetween 0.75 and 1.1 kg/dm³, and can be selected, for example, from: gasoils for use as automotive fuels or for production of heat, fuel oils,kerosenes, aviation fuels (Jet Fuels).

[0052] The amount of water to be emulsified with the liquid hydrocarbonis determined so as to obtain the desired reduction in pollutantswithout, however, impairing the calorific yield for the combustionprocess. This amount is generally between 3 and 40% by weight,preferably between 7 and 20% by weight, relative to the total weight ofthe fuel. The water used can be of any type, for example industrial ordomestic mains water. However, it is preferred to use demineralized ordeionized water, in order to avoid the deposition of mineral salts onthe internal surface of the combustion chamber and/or on the injectors.

[0053] The fuel according to the present invention can contain otheradditives, whose nature and amount depend on the specific use for whichthe fuel is intended. These additives can be selected, for example,from: cetane improvers, corrosion inhibitors, lubricants, biocides,antifoaming agents and antifreezes.

[0054] In particular, the cetane improvers are products which improvethe detonating properties of the fuel, and are generally selected fromnitrates, nitrites and peroxides of organic or inorganic nature, whichare soluble in the aqueous phase or, preferably, soluble in thehydrocarbon phase, such as organic nitrates (see for example patentsEP-475 620 and U.S. Pat. No. 5,669,938). Of preferred use are alkyl orcycloalkyl nitrates containing up to 10 carbon atoms, such as: ethylnitrate, amyl nitrates, n-hexyl nitrate, 2-ethylhexyl nitrate, n-decylnitrate, cyclohexyl nitrate and the like, or mixtures thereof.

[0055] The biocides can be selected from those known in the art, such asmorpholine derivatives, isothiazolin-3-one derivatives,tris(hydroxymethyl)-nitromethane, formaldehyde and the like, or mixturesthereof.

[0056] The fuel according to the present invention can also include analcohol, which, by lowering the freezing point of the aqueous phase,serves mainly as an antifreeze. Alcohols which are suitable for thispurpose are, for example: methanol, ethanol, isopropanol and glycols, ormixtures thereof. The amount of alcohol is generally between 0.5 and 8%by weight, preferably between 1 and 4% by weight, relative to the totalweight of the fuel.

[0057] The fuel according to the present invention is generally preparedby mixing the components using an emulsifying device known in the art,in which the formation of the emulsion can result from a mechanical-typeaction exerted by moving parts, or from passing the components to beemulsified into mixing devices of static type, or alternatively from acombined mechanical and static action. The emulsion is formed by feedingthe aqueous phase and the hydrocarbon phase, optionally premixed, intothe emulsifying device. The emulsifier and the other additives which maybe present can be introduced separately or, preferably, premixed eitherin the aqueous phase or in the hydrocarbon phase depending on theirsolubility properties. Preferably, the polymeric surfactant is premixedin the hydrocarbon phase.

[0058] The present invention will now be further illustrated by means ofsome working examples.

EXAMPLE 1

[0059] A. Preparation of Polyethylene Glycol Monoester (PEG-Monoester)

[0060] 300 g of an oleic acid/linoleic acid mixture in a 60/40 weightratio and 400 g of polyethylene glycol (PEG) (molecular weight (MW): 400g/mol) were mixed together in a reactor. 3.5 g of methanesulphonic acidas condensation catalyst and 340 ml of toluene as diluent (forming anazeotrope with H₂O) were added under stirring. The mixture was heatedgradually to 140° C. for a total time of about 5 hours, withdistillation and separation of the H₂O/toluene azeotrope. After furtherheating at 160° C. for 2 hours with distillation of the residualtoluene, the resulting product was degassed under vacuum for about 2hours at 140° C. The residual acidity was 4.5 mg of KOH per gram ofproduct.

[0061] B. Synthesis of the Polyisobutene Derivative by Reaction withMaleic Anhydride

[0062] 95 of polyisobutene (PIB) (average MW: 950 g/mol) with an exodouble bond content ≧90% (Ultravis® 10 from BP Amoco Chemicals), 9.4 gof maleic anhydride and 37 ml of xylene were loaded into a 500 mlTeflon® autoclave. After degassing with nitrogen, the autoclave washeated to a temperature of 190° C. and kept at this temperature for atotal of 22 hours. At the end of the reaction, the autoclave was cooledto 70° C. and degassed under vacuum for about 2 hours. The product thusobtained (101 g), a viscous yellow liquid, had a polyisobuteneconversion yield equal to about 43% (determined by chromatography onsilica using hexane as eluant) and an anhydride number (number of molesof bonded anhydride per 100 g of product) (determined by quantitativeinfrared spectroscopic analysis, based on the absorption peak at 1760cm⁻¹) of 0.052.

[0063] C. Synthesis of the Polymeric Surfactant

[0064] The PIB functionalized with maleic anhydride obtained fromreaction B (52.6 g) was loaded into a reactor and heated to about 50°C., followed by addition, with stirring, of xylene (5 g) and thePEG-monoester obtained from reaction A (75 g). The solution obtained washeated at 140° C. for 1 hour. The temperature was then maintained at180° C. for 10 hours, with distillation and separation of the H₂O/xyleneazeotrope. The product thus obtained, a slightly brown-coloured viscousliquid, had a residual acidity of 5.1 mg of KOH per gram of product.

EXAMPLE 2

[0065] 1000 g of an emulsion between diesel fuel and water were preparedusing the product of reaction C as emulsifier.

[0066] 18.87 g of the emulsifier obtained in Example 1C were added to865 g of automotive diesel fuel of EN590 type, to which 0.565 g of2-ethylhexyl nitrate (cetane improver) had been added beforehand. Themixture was subjected to the action of an IKA mechanical emulsifier fora few minutes, followed by addition of 115.00 g of water to which 0.565g of a bactericide (isothiazolin-3-one derivative) had been addedbeforehand. The emulsifier was then switched to the maximum stirringspeed for about 3 minutes. An emulsion having the composition below wasthus obtained: diesel fuel 86.5% by weight water 11.5% ″ emulsifier 1.887% ″ cetane improver  0.0565% ″ bactericide  0.0565% ″

EXAMPLE 3 (COMPARATIVE)

[0067] 1000 g of emulsion were prepared according to the same procedureas that described in Example 2, the only difference being the use,instead of the emulsifier of Example 1, of 18.87 g of a surfactantmixture consisting of 87% by weight of sorbitan monooleate, 3% by weightof sorbitan trioleate and 10% by weight of ethoxylated castor oil (10mol of ethylene oxide).

EXAMPLE 4

[0068] The emulsions prepared according to Examples 2 and 3 werecharacterized as follows.

[0069] Stability on Centrifugation

[0070] The stability of the emulsions was evaluated by centrifugation.Two series of tests were carried out, the first with freshly preparedemulsions (t=0) and the second after storing the emulsions at roomtemperature for 24 hours (t=24 h).

[0071] A graduated test tube was filled with 15 ml of emulsion. The testtube was placed in a centrifuge running at 4000 revolutions/min (equalto 2525 g; g=gravity acceleration) for a total time of 30 min, at roomtemperature. The amount, expressed as % by volume, of water-rich phasewhich separated at the bottom of the test tube (creaming) was measuredat regular intervals of 5 minutes of centrifugation.

[0072] The results for the emulsions of Examples 2 and 3 are given inTable 1.

[0073] Static Stability Under Temperature Cycle

[0074] The storage stability of the emulsions was evaluated by thefollowing method.

[0075] A 1000 ml glass cylinder filled with the test emulsion was placedin a thermostatically-controlled oven whose temperature was controlledaccording to the following temperature cycle: 8 hours at 40° C., 8 hoursat 20° C., 8 hours at 5° C. The emulsion was subjected to thistemperature cycle for 14 days. 15 ml samples were then taken from thetop and the bottom of the emulsion, and were used to determine the watercontent by means of Karl-Fisher titration according to ISO standard3734. The same measurements were carried out on a sample subjected tothe temperature cycle for 28 days.

[0076] The results for the emulsions of Examples 2 and 3 are given inTable 2 (values averaged over three samples), this table also showingthe variation of the water content relative to the reference value(t=0), measured on the freshly prepared emulsion.

[0077] As can be seen from the data given in Tables 1 and 2, theemulsion according to the invention shows high stability tocentrifugation and to the temperature cycles, whereas in the emulsionaccording to the prior art, the aqueous phase tends to settle in largeamounts.

[0078] Formation of Deposits on Metal Plate

[0079] A stainless steel plate (10 cm×5 cm) was placed on a heatingplate maintained at a temperature of about 280-300° C. On reaching thistemperature, one drop of emulsion was placed on the steel plate every 30seconds, for a total of 10 drops. After depositing the final drop, theplate was cooled for a further 30 seconds. The formation of acarbonaceous deposit was observed on the plate. The test is to beconsidered as positive if this deposit can be easily wiped off in asubstantially complete manner by rubbing with a dry cloth, while thetest is negative if much of the deposit still sticks to the plate evenafter prolonged rubbing.

[0080] The test carried out with the emulsion according to the invention(Ex. 2) gave a positive result, with formation of a thin deposit whichwas easily removed by rubbing. In contrast, the comparative emulsion(Ex. 3) failed the test, since it formed a dark deposit which could notbe removed by rubbing.

[0081] Lubricity. Corrosion.

[0082] Compared with diesel fuel as such, the emulsion according to theinvention (Ex. 2) showed a lubricity (measured according to ISO standard12156/1) of 270 μm, compared with a value of 385 μm for diesel fuel assuch. Thus, the emulsion according to the invention has better anti-gripcapacity than diesel fuel as such.

[0083] Evaluation of the corrosion according to standard EN590classified the emulsion according to the invention in Class 1a, equal tothat of diesel fuel as such. TABLE 1 Emulsion t = 0 Ex. 2 centrifugation5 10 15 20 25 30 (inv.) time (min) creaming 0.53 1.33 2.00 2.67 3.003.67 (% vol) t = 24 h centrifugation 5 10 15 20 25 30 time (min)creaming 0.53 1.00 1.67 2.00 2.67 3.33 (% vol) Emulsion t = 0 Ex. 3centrifugation 5 10 15 20 25 30 (comp.) time (min) creaming 3.33 6.006.67 8.00 9.00 9.67 (% vol) t = 24 h centrifugation 5 10 15 20 25 30time (min) creaming 6.67 9.33 10.00 10.33 10.67 11.00 (% vol)

[0084] TABLE 2 H₂O content H₂O content at the top at the bottomVariation Variation Time (% by (% by top bottom Emulsion (days) weight)weight) (%) (%) Ex. 2 0 11.54 — — (inv.) 14 11.05 12.22 −4.2 +5.9 2810.99 13.35 −4.8 +15.7 Ex. 3 0 10.92 — — (comp.) 14 6.06 42.31 −44.5+287 28 1.74 62.46 −84.1 +472

EXAMPLE 5

[0085] 1000 g of an emulsion between fuel oil and water were preparedusing the product of reaction C as emulsifier.

[0086] 5.00 g of the emulsifier obtained in Example 1C were added to 845g of Denso BTZ fuel oil, corresponding to Italian UNI standard6579:1998. After subjecting the mixture to the action of an IKAmechanical emulsifier for a few minutes, 150 g of water were added. Theresulting emulsion had the following composition: fuel oil 84.5% byweight water 15% ″ emulsifier  0.5% ″

EXAMPLE 6 (COMPARATIVE)

[0087] 1000 g of emulsion were prepared according to the same procedureas that described in Example 5, the only difference being the use,instead of the emulsifier of Example 1, of 5.00 g of a surfactantmixture consisting of 87% by weight of sorbitan monooleate, 3% by weightof sorbitan trioleate and 10% by weight of ethoxylated castor oil (10mol of ethylene oxide).

EXAMPLE 7

[0088] The emulsions prepared according to Examples 5 and 6 werecharacterized as follows.

[0089] Static Stability at 50° C.

[0090] The storage stability of the emulsions was evaluated by thefollowing method.

[0091] A 1000 ml glass cylinder filled with the test emulsion was placedin a thermostatically-controlled oven at a temperature of 50° C.±3° C.After leaving it in the oven for 90 days, a 15 ml sample was taken fromthe top of the emulsion and its water content was determined byKarl-Fisher titration according to ISO standard 3734.

[0092] The surface water content measured for the emulsion according tothe invention (Ex. 5) was 13.0% by weight, with a difference of 2%relative to the initial value, whereas for the comparative emulsion (Ex.6) the amount of water at the top was less than 1% by weight.

[0093] The results of the tests demonstrate that the emulsion accordingto the invention displays substantial stability even after a prolongedperiod of storage under warm conditions, whereas in the comparativeemulsion the water tends to separate out and become deposited at thebottom.

1. Fuel comprising an emulsion between water and a liquid hydrocarbon,said emulsion being stabilized by an emulsifier, characterized in thatthe said emulsifier is a polymeric surfactant obtainable by reactionbetween: (i) a polyolefin oligomer functionalized with at least onegroup deriving from a dicarboxylic acid, or a derivative thereof; and(ii) a polyoxyalkylene comprising linear oxyalkylene units, saidpolyoxyalkylene being linked to a long-chain alkyl group optionallycontaining one or-more ethylenic unsaturations.
 2. Fuel according toclaim 1, wherein the polyolefin oligomer has an average molecular weightof from 300 to 10,000.
 3. Fuel according to claim 2, wherein thepolyolefin oligomer has an average molecular weight of from 500 to 5000.4. Fuel according to any one of the preceding claims, wherein thepolyolefin oligomer derives from polymerization of mixtures of olefinshaving 4 carbon atoms, and mainly contains isobutene repeating units offormula:


5. Fuel according to any one of the preceding claims, wherein thepolyoxyalkylene is a polyoxy-ethylene having from 2 to 40 oxyethyleneunits of formula —CH₂CH₂O—.
 6. Fuel according to claim 5, wherein thepoly-oxyethylene has from 5 to 20 oxyethylene units.
 7. Fuel accordingto any one of claims 1 to 4, wherein the polyoxyalkylene is a copolymerhaving from 2 to 30 oxyethylene units of formula —CH₂CH₂O—, and not morethan 12 branched oxyethylene units of formula:

wherein R₁ is an alkyl having from 1 to 3 carbon atoms.
 8. Fuelaccording to claim 7, wherein R₁ is methyl.
 9. Fuel according to any oneof the preceding claims, wherein the polyoxyalkylene is linked to along-chain alkyl group, of linear or branched structure, optionallycontaining one or more ethylenic unsaturations, having from 8 to 24carbon atoms.
 10. Fuel according to any one of the preceding claims,wherein the polyoxyalkylene is linked to the long-chain alkyl group viaan ester group.
 11. Fuel according to any one of claims 1 to 9, whereinthe polyoxyalkylene is linked to the long-chain alkyl group via an ethergroup.
 12. Fuel according to any one of the preceding claims, whereinthe polyolefin oligomer is functionalized by reaction with adicarboxylic acid derivative selected from: acyl halides, C₁-C₄ estersand anhydrides.
 13. Fuel according to any one of the preceding claims,wherein the functionalized polyolefin oligomer is obtained by reactionbetween maleic anhydride and a polyisobutene containing not less than65% of exo double bonds.
 14. Fuel according to any one of the precedingclaims, wherein the polymeric surfactant is present in an amount ofbetween 0.1 and 5% by weight relative to the total weight of the fuel.15. Fuel according to claim 14, wherein the polymeric surfactant ispresent in an amount of between 0.5 and 3% by weight relative to thetotal weight of the fuel.
 16. Fuel according to any one of the precedingclaims, wherein the liquid hydrocarbon has a viscosity at 40° C. ofbetween 1 and 53 cSt and a density at 15° C. of between 0.75 and 1.1kg/dm³.
 17. Fuel according to any one of the preceding claims; whereinthe water is present in an amount of between 3 and 40% by weightrelative to the total weight of the fuel.
 18. Fuel according to claim17, wherein the water is present in an amount of between 7 and 20% byweight relative to the total weight of the fuel.
 19. Fuel according toany one of the preceding claims, also comprising at least one cetaneimprover.
 20. Fuel according to claim 19, wherein said at least onecetane improver is selected from nitrates, nitrites and peroxides ofinorganic nature.
 21. Fuel according to claim 19, wherein said at leastone cetane improver is selected from nitrates, nitrites and peroxides oforganic nature.
 22. Fuel according to any one of the preceding claims,also comprising at least one biocide.
 23. Fuel according to any one ofthe preceding claims, also comprising at least one alcohol.
 24. Fuelaccording to claim 23, wherein the alcohol is selected from: methanol,ethanol, isopropanol and glycols, or mixtures thereof.
 25. Fuelaccording to claim 24, wherein the alcohol is present in an amount ofbetween 0.5 and 8% by weight relative to the total weight of the fuel.26. Fuel according to claim 25, wherein the alcohol is present in anamount of between 1 and 4% by weight relative to the total weight of thefuel.
 27. Process for fueling a combustion apparatus comprising at leasta combustion chamber, comprising: feeding a fuel to said at least onecombustion chamber; igniting said fuel in said at least one combustionchamber; wherein said fuel comprises an emulsion between water and aliquid hydrocarbon according to anyone of claims from 1 to
 26. 28.Process according to claim 27, wherein said combustion apparatus is aninternal combustion engine.